The php5-uuid functions could definitely use some documentation to clarify how they should be used, but here's what I've gleaned by examining the OSSP source code (found here: http://ossp-uuid.sourcearchive.com/documentation/1.5.1-1ubuntu1/php_2uuid_8c-source.html).

The uuid_make() function takes two arguments when generating v1 or v4, but four arguments are required when generating v3 or v5. The first two arguments have been demonstrated below and are straightforward, so I'll skip to the as-yet non-described arguments.

The third argument to uuid_make() is: $namespace
  - this is a secondary resource created with uuid_create(); it is apparently used to generate an internal UUID, which is used as the namespace of the output UUID

The fourth argument to uuid_make() is: $url
  - this is the value that is to be hashed (MD5 for v3, SHA-1 for v5); it may be any string or even null

Here's a simple class illustrating the proper usage (note that if php5-uuid is not installed on your system, each function call will just return false):

<?php
class UUID {
  /**
   * Generates version 1: MAC address
   */
  public static function v1() {
    if (!function_exists('uuid_create'))
      return false;

    uuid_create(&$context);
    uuid_make($context, UUID_MAKE_V1);
    uuid_export($context, UUID_FMT_STR, &$uuid);
    return trim($uuid);
  }

  /**
   * Generates version 3 UUID: MD5 hash of URL
   */
  public static function v3($i_url) {
    if (!function_exists('uuid_create'))
      return false;

    if (!strlen($i_url))
      $i_url = self::v1();

    uuid_create(&$context);
    uuid_create(&$namespace);

    uuid_make($context, UUID_MAKE_V3, $namespace, $i_url);
    uuid_export($context, UUID_FMT_STR, &$uuid);
    return trim($uuid);
  }

  /**
   * Generates version 4 UUID: random
   */
  public static function v4() {
    if (!function_exists('uuid_create'))
      return false;

    uuid_create(&$context);

    uuid_make($context, UUID_MAKE_V4);
    uuid_export($context, UUID_FMT_STR, &$uuid);
    return trim($uuid);
  }

  /**
   * Generates version 5 UUID: SHA-1 hash of URL
   */
  public static function v5($i_url) {
    if (!function_exists('uuid_create'))
      return false;

    if (!strlen($i_url))
      $i_url = self::v1();

    uuid_create(&$context);
    uuid_create(&$namespace);

    uuid_make($context, UUID_MAKE_V5, $namespace, $i_url);
    uuid_export($context, UUID_FMT_STR, &$uuid);
    return trim($uuid);
  }
}
?>

And here's a demonstration:

<?php
for ($i = 1; $i <= 3; ++$i) {
  echo 'microtime = ' . microtime(true) . '<br/>';
  echo "V1 UUID: " . UUID::v1() . '<br/>';
  echo "V3 UUID of URL='abc': " . UUID::v3('abc') . '<br/>';
  echo "V4 UUID: " . UUID::v4() . '<br/>';
  echo "V5 UUID of URL=null: " . UUID::v5(null) . '<br/>';
  echo '<hr/>';
}
?>